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Friday, February 12, 2010

Genetics: Introduction concepts

Inheritance Patterns

Mendel was the first scientist to develop a method for predicting the outcome of inheritance patterns. He performed his work with pea plants, studying seven traits: plant height, pod shape, pod color, seed shape, seed color, flower color, and flower location. Pea plants pollinate themselves. Therefore, over many generations, pea plants develop individuals that are homozygous for particular characteristics. These populations are known as pure lines.

In his work, Mendel took pure-line pea plants and cross-pollinated them with other pure-line pea plants. He called these plants the parent generation. When Mendel crossed pure-line tall plants with pure-line short plants, he discovered that all the plants resulting from this cross were tall. He called this generation the F1 generation (first filial generation). Next, Mendel crossed the offspring of the F1 generation tall plants among themselves to produce a new generation called the F2 generation (second filial generation). Among the plants in this generation, Mendel observed that three-fourths of the plants were tall and one-fourth of the plants were short.

Mendel's laws of genetics
Mendel conducted similar experiments with the other pea plant traits. Over many years, he formulated several principles that are known today as Mendel's laws of genetics. His laws include the following:

1. Mendel's law of dominance: When an organism has two different alleles for a trait, one allele dominates.
2. Mendel's law of segregation: During gamete formation by a diploid organism, the pair of alleles for a particular trait separate, or segregate, during the formation of gametes (as in meiosis).
3. Mendel's law of independent assortment: The members of a gene pair separate from one another independent of the members of other gene pairs. (These separations occur in the formation of gametes during meiosis.)

 Genetics Part-I

DNA replication, transcription and translation.
In very general terms, what does a chromosome contain?

• Information, genetic information to carry out the characteristics of life -- precise self replication, ability to exchange energy with the environment, etc.

In very general terms, what are the two related functions of DNA?
• Information storage

• DNA replication

• Information transfer

• DNA transcribed into RNA

• DNA's function in information transfer

What is the Central Dogma associated with information storage and retrieval?

• Central Dogma:
DNA-->RNA-->unfolded protein-->native, folded protein

What are the three processes of the central dogma?
How does DNA function as an information molecule?

• replication, DNA --> DNA

• transcription, DNA --> RNA

• translation, RNA --> unfolded protein --> folded protein

In terms of molecular conformation, what occurs through the central dogma?

• Translation of linear information, a sequence of nucleotides, into 3-D information, the structure of a protein.

What are the differences between DNA and RNA?
• base composition: RNA = AGCU, DNA = AGCT

• carbohydrate: RNA = ribose, DNA = deoxyribose

• structure: RNA = single stranded, DNA = double helix


• usually single stranded

• linear polymer of ribonucleotides.

• Some secondary and tertiary structure but often ill-defined.

What are the different types of RNA?
What are the functions of the different types of RNA?

• messenger RNA = mRNA, information transfer

• transfer RNA = tRNA, information transfer

• ribosomal RNA = rRNA, structural

• small nuclear RNA = snRNA, ribozymes, RNA processing.
What is replication?

Transfer of genetic information from one generation to the next.

DNA-directed DNA synthesis: replication of the genome.

What is the structural basis for the precise duplication of the genome?
• The Watson-Crick structure of DNA: the strands are complementary, the nucleotide sequence in one automatically specifies the other.

• The enzyme, DNA polymerase III, is very accurate: it has proof reading capabilities.

Is replication conservative or semi-conservative? What does that mean?

• Is the parental genome of double stranded DNA fully conserved in the parental cell or is it split equally (semi-conserved) between two daughter cells?

• Replication is semi-conservative.

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